The present invention relates to a high pressure hose, built up of several layers, having generally a diameter greater than 50 mms and being suitable for conveying gases and gas-containing fluids.
It is known, that continually newer demands are made by technical developments to improve the technical products which are needed for the developments. Thus for example the development of marine oil mining has brought forth the demand for flexible hoses suitable for conveying the crude oil produced. Materials from underground sources such as crude oil, earth gas, water, H.sub.2 s and other aggressive materials flow through such hoses. These hoses have to show extraordinary complex properties, because the mentioned materials attack the hose from the inside with 100 atmospheres or even higher pressure and at the producing temperature of the well. At the same time the hose is exposed from the outside to the effect of sea-water in off shore wells; it has to bear the waves of the environment, for example the sea and the watercolumn-pressure corresponding to the depth of the sea. Besides there is the further problem, that standardization of the hoses cannot be practically accomplished since each well used to extract the mentioned materials creates different interior and exterior loads.
In the case of oil mining, especially "off-shore" mining in addition to stiff pipe systems flexible lines are also used. Various flexible pipes have been worked out for conveying gas-free oil. These hoses resist high-pressure and in special cases they resist the high axial pull-force and radial pressure-force (external pressure). Resistance to the listed loads are generally ensured with reinforcing ply systems of two main types. One of the ply systems consists of plies of even numbers, in which steel wires, profile wires or wire cords applied with a high pitch helically in opposite direction are placed under an angle. Resistance to radial forces (with hoses laid on the sea bottom) is increased with one or more plies formed from helically wound wires with a small pitch. The plies are connecting or non connecting steel profile bands or glass-resin banded systems. Resistance to axial pull force is given by the coworking of the above two ply systems. In order to separate the individual carcass reinforcing plies and embedding respectively, usually rubber or plastic layers are applied. The sealing ability of the hose is ensured by a rubber or plastic tube resisting the aggressive effect, such as high temperature of the medium to be conveyed because its heat resistance is higher, than the temperature of the medium. In addition the hose has an external rubber or plastic cover protecting the reinforcing plies from the corrosive effect of the external medium, e.g. water, air and sea water. Such hoses are described in French Pat. No. 2,210,266 as well as in the Hungarian Pat. Nos. 169,115 and 172,426.
Though the hoses described above are suitable for conveying gas-free oil they are not suitable for conveying a gas-containing medium. The reason for this is that the gas to be conveyed diffuses through tube layers made of plastics or synthetic rubber which are used to ensure sealing and penetrates among the structural elements of the hose, breaking them causing failure and blistering. Such a phenomenon is manifested by the bulging of the outer plastic or synthetic rubber cover layer, as well as the blistering of the internal tube after the cessation of the internal pressure of the medium to be conveyed.
For stopping the deteriorating effect of the gas diffused into the hose structure several methods have been developed. Thus, for example, for checking the bulging of the cover layer, this layer is pierced at several places enabling the escape of the gas accumulated underneath. Such a solution is described in French Pat. No. 2,286,331. The drawback of this method is, that the external environment such as moisture and, sea water can penetrate through the perforated holes as far as the steel wire plies and cause corrosion. According to another method the path of gas diffusion through the individual plastic or rubber layers is ensured by gradually increasing the gas permeability of the polymer layers situated outward from the tube. Such a method is disclosed in U.S. Pat. No. 4,120,324. The disadvantage of the above method is partly that in practice the adjustment of the permeability gradient is very difficult, since the choice of suitable raw materials resistant to the materials conveyed is very small. Part of the problem is that the material conveyed has generally a higher temperature than the environment, thus, in the hose a decreasing temperature gradient sets in and it is known that the rate of gas diffusion is greatly increased with increasing temperature.
Further methods are given in Swiss Pat. No. 569,909, in Austrian Pat. No. 331,593 and in the British Pat. No. 1,409,096, according to which the gas diffusion is prevented by a corrugated steel pipe situated as an internal layer of the hose. The draw back of this method is that the manufacturing process is difficult to accomplish, and the corrugated internal surface greatly increases the flow resistance of the material conveyed.
The object of the present invention is to develop a hose without having the disadvantages detailed in the foregoing. From the drawbacks of the known methods it is apparent that there is a need for a hose which can satisfactorily resist internal and external deteriorating effects caused by the external environment and the medium flowing therethrough.